Ādi(Adi) is one of the names of God Śiva-Mahādeva9Siva-Mahadeva), mentioned in Śivasahasranāmastotra (Sivasahasranamastotra; The Hymn of the Thousand Names of Siva). He has also been addressed as Ādya (Adya). The commentator, Nīlakaṇṭha (Nilakantha), has thus analysed the meaning of the name Ādi —
ādi sarvasmāt prathamaḥ.
The same idea has been expressed in the clarification of the name, Ādya(Adya) —
ādyaḥ saṁsārāt prāchīnaḥ.
While analysing the meaning of the name Ādikara (Adikara), we have already discussed that in the beginning of Creation, Prajāpati, Creator of the universe, emerged at first. And the whole universe was created out of Him. But the formless, motionless Brahman that is conceptualised in the Upaniṣad (Upanishad), is the Creator of Hiraṇyagarbha (Hiranyagarbha; the Golden-wombed) Prajāpati (Prajapati; Ruler of the people); and he is the Primary Self. He has no beginning and no end. During the time of Pralaya, when all creations get destroyed, Prajāpati (Prajapati) himself get dissolved in the Brahman, who is beyond creation and destruction. The name Ādi refers to the absolute Self of Mahādeva as Brahman.
In Bhagavadgītā (Bhagavadgita), Srī Kṛṣṇa (Sri Krishna), in course of describing His Supreme Self as Parameśvara, says ‘Even the gods and sages do not know about my emergence, because I am the Ādi and the cause of all creations in the universe’–
na me viduḥ suragaṇāḥ prabhavaṁ na maharṣayaḥ
ahamādihi devānāṁ maharṣiṇāñca sarvaśaḥ.

In another śloka (sloka; verse), He says, ‘I am the Supreme Self residing in all living and non-living objects. I am the beginning, the middle and the end of this creation, and I am the fundamental cause of the creation’ —
ahamātmā guḍākeśa sarvabhūtāśayasthitaḥ
ahamādiśca madhyañca bhūtānāmanta eva ca.

The Brahman whose nature and existence of Self is described in the Upaniṣad, has come to be identified with Krṣṇa or Viṣnu-Nārāyaṇa (Vishnu-Narayana) , and sometimes with Rudra-Śiva, in Mahākāvya(Mahakavya; epic) and the Purāṇas (Purana, Mythological Scriptures). Through this idea, both Śiva and Kṛṣṇa become one with the Ādipuruṣa(Adipurusha) described in Bhagavadgītā.